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<title>18.5.1 URLopener Objects </title>
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<h2><a name="SECTION0020510000000000000000"></a><a name="urlopener-objs"></a>
<br>
18.5.1 URLopener Objects 
</h2>

<p>
<tt class="class">URLopener</tt> and <tt class="class">FancyURLopener</tt> objects have the
following attributes.

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3921' xml:id='l2h-3921' class="method">open</tt></b>(</nobr></td>
  <td><var>fullurl</var><big>[</big><var>, data</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Open <var>fullurl</var> using the appropriate protocol.  This method sets
up cache and proxy information, then calls the appropriate open method with
its input arguments.  If the scheme is not recognized,
<tt class="method">open_unknown()</tt> is called.  The <var>data</var> argument
has the same meaning as the <var>data</var> argument of <tt class="function">urlopen()</tt>.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3922' xml:id='l2h-3922' class="method">open_unknown</tt></b>(</nobr></td>
  <td><var>fullurl</var><big>[</big><var>, data</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Overridable interface to open unknown URL types.
</dl>

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3923' xml:id='l2h-3923' class="method">retrieve</tt></b>(</nobr></td>
  <td><var>url</var><big>[</big><var>,
                                        filename</var><big>[</big><var>,
                                        reporthook</var><big>[</big><var>, data</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Retrieves the contents of <var>url</var> and places it in <var>filename</var>.  The
return value is a tuple consisting of a local filename and either a
<tt class="class">mimetools.Message</tt> object containing the response headers (for remote
URLs) or <code>None</code> (for local URLs).  The caller must then open and read the
contents of <var>filename</var>.  If <var>filename</var> is not given and the URL
refers to a local file, the input filename is returned.  If the URL is
non-local and <var>filename</var> is not given, the filename is the output of
<tt class="function">tempfile.mktemp()</tt> with a suffix that matches the suffix of the last
path component of the input URL.  If <var>reporthook</var> is given, it must be
a function accepting three numeric parameters.  It will be called after each
chunk of data is read from the network.  <var>reporthook</var> is ignored for
local URLs.

<p>
If the <var>url</var> uses the <span class="file">http:</span> scheme identifier, the optional
<var>data</var> argument may be given to specify a <code>POST</code> request
(normally the request type is <code>GET</code>).  The <var>data</var> argument
must in standard <span class="mimetype">application/x-www-form-urlencoded</span> format;
see the <tt class="function">urlencode()</tt> function below.
</dl>

<p>
<dl><dt><b><tt id='l2h-3924' xml:id='l2h-3924' class="member">version</tt></b></dt>
<dd>
Variable that specifies the user agent of the opener object.  To get
<tt class="module"><a href="module-urllib.html">urllib</a></tt> to tell servers that it is a particular user agent,
set this in a subclass as a class variable or in the constructor
before calling the base constructor.
</dl>

<p>
The <tt class="class">FancyURLopener</tt> class offers one additional method that
should be overloaded to provide the appropriate behavior:

<p>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-3925' xml:id='l2h-3925' class="method">prompt_user_passwd</tt></b>(</nobr></td>
  <td><var>host, realm</var>)</td></tr></table></dt>
<dd>
Return information needed to authenticate the user at the given host
in the specified security realm.  The return value should be a tuple,
<code>(<var>user</var>, <var>password</var>)</code>, which can be used for basic
authentication.

<p>
The implementation prompts for this information on the terminal; an
application should override this method to use an appropriate
interaction model in the local environment.
</dl>

<p>

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